diff --git a/content/base/src/nsGkAtomList.h b/content/base/src/nsGkAtomList.h
index 53162fee49c..a680b6c381b 100644
--- a/content/base/src/nsGkAtomList.h
+++ b/content/base/src/nsGkAtomList.h
@@ -609,7 +609,6 @@ GK_ATOM(mozfullscreenerror, "mozfullscreenerror")
 GK_ATOM(mozpasspointerevents, "mozpasspointerevents")
 GK_ATOM(mozpointerlockchange, "mozpointerlockchange")
 GK_ATOM(mozpointerlockerror, "mozpointerlockerror")
-GK_ATOM(mozprivatebrowsing, "mozprivatebrowsing")
 GK_ATOM(moz_opaque, "moz-opaque")
 GK_ATOM(moz_action_hint, "mozactionhint")
 GK_ATOM(x_moz_errormessage, "x-moz-errormessage")
diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index 94d3d12a787..f7e1d7df4a3 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -851,7 +851,6 @@ nsDocShell::nsDocShell():
 #endif
     mAffectPrivateSessionLifetime(true),
     mInvisible(false),
-    mHasLoadedNonBlankURI(false),
     mDefaultLoadFlags(nsIRequest::LOAD_NORMAL),
     mFrameType(eFrameTypeRegular),
     mOwnOrContainingAppId(nsIScriptSecurityManager::UNKNOWN_APP_ID),
@@ -1929,10 +1928,6 @@ nsDocShell::SetCurrentURI(nsIURI *aURI, nsIRequest *aRequest,
 
     mCurrentURI = NS_TryToMakeImmutable(aURI);
     
-    if (!NS_IsAboutBlank(mCurrentURI)) {
-      mHasLoadedNonBlankURI = true;
-    }
-
     bool isRoot = false;   // Is this the root docshell
     bool isSubFrame = false;  // Is this a subframe navigation?
 
@@ -2282,15 +2277,6 @@ nsDocShell::SetPrivateBrowsing(bool aUsePrivateBrowsing)
     return NS_OK;
 }
 
-NS_IMETHODIMP
-nsDocShell::GetHasLoadedNonBlankURI(bool* aResult)
-{
-    NS_ENSURE_ARG_POINTER(aResult);
-
-    *aResult = mHasLoadedNonBlankURI;
-    return NS_OK;
-}
-
 NS_IMETHODIMP
 nsDocShell::GetUseRemoteTabs(bool* aUseRemoteTabs)
 {
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index d9a82abe4f7..eda8f221558 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -915,7 +915,6 @@ protected:
 #endif
     bool                       mAffectPrivateSessionLifetime;
     bool                       mInvisible;
-    bool                       mHasLoadedNonBlankURI;
     uint64_t                   mHistoryID;
     uint32_t                   mDefaultLoadFlags;
 
diff --git a/docshell/base/nsIDocShell.idl b/docshell/base/nsIDocShell.idl
index cf81b57427e..02c07d548dd 100644
--- a/docshell/base/nsIDocShell.idl
+++ b/docshell/base/nsIDocShell.idl
@@ -54,7 +54,7 @@ interface nsITabParent;
  
 typedef unsigned long nsLoadFlags;
 
-[scriptable, builtinclass, uuid(23157a63-26fd-44a0-a0f9-fdc64dcc004c)]
+[scriptable, builtinclass, uuid(2b8e4a50-7744-454d-a05b-debead8070fe)]
 interface nsIDocShell : nsIDocShellTreeItem
 {
   /**
@@ -1017,11 +1017,4 @@ interface nsIDocShell : nsIDocShellTreeItem
 
   // URLSearchParams for the window.location is owned by the docShell.
   [noscript,notxpcom] URLSearchParams getURLSearchParams();
-
-  /**
-   * This attribute determines whether a document which is not about:blank has
-   * already be loaded by this docShell.
-   */
-  [infallible] readonly attribute boolean hasLoadedNonBlankURI;
-
 };
diff --git a/dom/browser-element/BrowserElementChild.js b/dom/browser-element/BrowserElementChild.js
index 4996b178e0f..aa06587c95f 100644
--- a/dom/browser-element/BrowserElementChild.js
+++ b/dom/browser-element/BrowserElementChild.js
@@ -56,10 +56,3 @@ let infos = sendSyncMessage('browser-element-api:call',
                             { 'msg_name': 'hello' })[0];
 docShell.QueryInterface(Ci.nsIDocShellTreeItem).name = infos.name;
 docShell.setFullscreenAllowed(infos.fullscreenAllowed);
-if (infos.isPrivate) {
-  if (docShell.hasLoadedNonBlankURI) {
-    Cu.reportError("We should not switch to Private Browsing after loading a document.");
-  } else {
-    docShell.QueryInterface(Ci.nsILoadContext).usePrivateBrowsing = true;
-  }
-}
diff --git a/dom/browser-element/BrowserElementParent.cpp b/dom/browser-element/BrowserElementParent.cpp
index 83f5057ba4d..62ca3c119d1 100644
--- a/dom/browser-element/BrowserElementParent.cpp
+++ b/dom/browser-element/BrowserElementParent.cpp
@@ -76,14 +76,6 @@ CreateIframe(Element* aOpenerFrameElement, const nsAString& aName, bool aRemote)
                                        NS_LITERAL_STRING("false"),
                              /* aNotify = */ false);
 
-  // Copy the opener frame's mozprivatebrowsing attribute to the popup frame.
-  nsAutoString mozprivatebrowsing;
-  if (aOpenerFrameElement->GetAttr(kNameSpaceID_None, nsGkAtoms::mozprivatebrowsing,
-                                   mozprivatebrowsing)) {
-    popupFrameElement->SetAttr(kNameSpaceID_None, nsGkAtoms::mozprivatebrowsing,
-                               mozprivatebrowsing, /* aNotify = */ false);
-  }
-
   return popupFrameElement.forget();
 }
 
diff --git a/dom/browser-element/BrowserElementParent.jsm b/dom/browser-element/BrowserElementParent.jsm
index 3a7124be800..066c59a040a 100644
--- a/dom/browser-element/BrowserElementParent.jsm
+++ b/dom/browser-element/BrowserElementParent.jsm
@@ -389,8 +389,7 @@ BrowserElementParent.prototype = {
       name: this._frameElement.getAttribute('name'),
       fullscreenAllowed:
         this._frameElement.hasAttribute('allowfullscreen') ||
-        this._frameElement.hasAttribute('mozallowfullscreen'),
-      isPrivate: this._frameElement.hasAttribute('mozprivatebrowsing')
+        this._frameElement.hasAttribute('mozallowfullscreen')
     };
   },